1. Field of the Invention
The present invention relates to modified pigment products and dispersions, black matrixes, and resin compositions comprising these modified pigment products.
2. Description of the Related Art
Black matrix is a generic name for materials used in color displays to improve the contrast of an image by separating individual color pixels. In liquid crystal displays (LCDs), the black matrix is a thin film having high light-shielding capability and is formed between the three color elements of a color filter. In LCD's using thin film transistors (TFT), the black matrix also prevents the formation of photo-induced currents due to reflected light in the TFT.
Conventionally the black matrix layer in liquid crystal displays is manufactured by vapor deposition of Cr/CrO. Although chromium based films have excellent light-shielding capabilities, the metal vapor deposition process is expensive. In addition, chromium use and disposal is subject to increasingly restrictive environmental regulations. Chromium films also have low resistivity, which restricts the electrical design of LCDs to a subset of the possible design configurations.
Black pigments such as carbon black have been used in polymer compositions to make resistive black matrixes. However, typical systems have not been able to provide the desired balance of overall properties. For example, while a black matrix containing a carbon black pigment could provide the required light-shielding capabilities (that is, an optical density (OD) of greater than 3 at 1 micron thickness), typically the film would have only a modest resistivity. Alternatively, if a highly resistive film were produced, the OD was typically low.
Modified pigments having attached organic groups have also been disclosed for use in a black matrix for color filters. While these materials provide black matrixes and dispersions with good overall performance, there remains a need for black matrixes with improved properties, in particular, resistivity and optical density.